2 PROCEEDIlS'GS OF THE NATIONAL MUSEUM: vol.54. 



valve, where the tegmentum extends well forward mesially. Tail 

 valve lower and a trifle narrower than the head valve, the flaring 

 margin rendering the posterior slope distinctly concave; central area 

 mildly convex, the anterior margin arcuate; mucro a little in front 

 of the center. 



Anterior valve with a sculpture comprising a large number of 

 small, sharp, conical granules of ovate outline, very closely placed 

 with a greater or less quincuncial arrangement, so that there often 

 appear evidences of a secondary ranking of the granules in series 

 oblique to the lines of growth. Intermediate valves with distinct 

 lateral areas, the mesial regions of the latter somewhat sunken, but 

 their anterior margins raised to form a pseudo-rib; finer sculpture of 

 lateral areas very similar to that of the head valve; central areas 

 everywhere except in the immediate vicinity of the beaks covered 

 with a copious fine file-like sculpture of crowded, but distinct and 

 rarely overlapping pustules like those described except, that toward 

 the sides they show a quite definite arrangement in longitudinal lines 

 (these lines being roughly continuous with the less definite and more 

 oblique series of the lateral areas in a manner not brought out in the 

 drawing). The posterior valve corresponds in sculpture to the 

 remainder of the shell (pi. 1, fig. 1). 



Interior of head valve simple, but quite heavily calloused near the 

 margin. Intermediate valves with sutural laminae well separated, 

 broadly triangular, acute in front, and attached beneath the tegmen- 

 tum in such a way that the latter projects over somewhat at the base 

 and there is a notch giving a false appearance of slitting at the sides; 

 anterior sinus broad at the base, not quite as wide as the adjoining 

 laminae. Posterior valve with a rather heavj?" callus at the margin 

 and another supporting the sutural laminae which are shorter and 

 have more rounded margins than those of the intermediate valves 

 (pi. 2, fig. 2). 



Girdle with a dorsal armature of smaU, close-set spines, usually 

 very even in size, but occasionally both at the margin and elsewhere 

 a few scattered dagger-like spines, two or three times the length of 

 the commoner ones, may be noted (pi. 1, fig. 3; pi. 2, fig. 5). With 

 rather frequent exceptions all the spines show an outward trend. 

 No striation can be detected with such magnification as I have been 

 able to use. The spinelets of the ventral surface differ in their close 

 palisading, smaller size, more conical outline, and even greater uni- 

 formity for any given region of the girdle (pi. 2, fig. 4). 



Radula with large, strongly bidentate second laterals, medians 

 smaU and mushroom-like in outline, first laterals small. My prepara- 

 tion of the radula did not prove satsfactory and the drawing merely 

 serves to indicate the main features (pi. 2, fig. 6). 



